Location of ribosomal protein genes impacts Vibrio cholerae in absence of simultaneous replication rounds.

ALFONSO SOLER BISTUE; SEBASTIAN AGUILAR-PIERLE; MARC GARCIA-GARCERA ; DIDIER MAZEL

Roskoff

Congreso; The Vibrio Meeting 2016; 2016

The effect of gene order within the bacterial chromosome on cell physiology is poorly understood.In silico approaches have shown that ribosomal protein genes (RP) locate near the replication origin (oriC) only in fast-growing bacteria. Such apositional bias may be an evolutionary conserved growth-optimization strategy. Thus, bacteria would benefit from a higher RP dosage during exponential phase due to simultaneous replication rounds. We focused on S10-spc-alpha locus (S10),encoding half of the ribosomal proteins, in Vibrio cholerae, one of the fastest growing bacteria, to address this issue. Using recombineering tools, we systematically relocate this locus to alternative genomic positions. In fast growing conditions, S10 relative distance to the oriC tightly correlated with a reduction of its dosage, mRNA abundance and growth rate. In slow-growing conditions when multi-fork replication did not occur, no growth rate changes were noticed. Unexpectedly, competition experiments revealed lower fitness when RP are far from oriC showing that location of RP remains important. Strains bearing two S10 copies far from oriC rescued these phenotypes demonstrating that gene-dosage reduction is behind these alterations. To uncover putative mechanistic differences, DNA and RNA from this strain set were analyzed using Next Generation Sequencing approaches in slow and fast-growing conditions. During fast-growth the whole oriC region presented a reduced dosage showing concomitant reduction of its transcriptional activity. This phenomenon was not observed in slow growing conditions. Also,COGs and covariation analyses show that the functions altered were not shared between these culture conditions strongly suggesting different mechanisms behind these phenotypes. We propose that the impact of RP location on V.cholerae evolution goes beyond a growth-optimization strategy during feast periods. Contrary to expected, S10 location may be important along the whole life cycle. We suggest that RP positioning may also influence the evolution of slow-growing organisms.